The present invention relates to sol or gel compositions capable of enhancing the corrosion-protection properties of surface coating compositions and paints and particularly latex paints.
Surface coating compositions typically include such materials as paints, lacquers and varnishes. Paints contain pigmented materials whereas lacquers or varnishes are generally clear or transparent. The purposes of surface coatings are aesthetic and/or protective. A coating can enhance the appearance of a substrate in terms of color and gloss as well as give protection against such problems as weathering or corrosion.
In terms of corrosion protection, particularly corrosion protective properties relating to free metal-containing substrates, alternative and improved surface coatings or paints are still being sought. Free metal-containing substrates, particularly iron-containing substrates such as mild steel, cast iron, wrought iron, and the like, and others such as galvanized steel, aluminum, copper, brass, alloys thereof, etc., are vulnerable to exposure damage (i.e., corrosion) without some form of protection. Corrosion includes dry (oxidative) corrosion and stress corrosion. Surface coating defects related to corrosion include rusting, blistering, delamination, undercutting, under-rusting and film form corrosion. Some of the factors which influence the extent to which a surface coating composition or paint will protect metal-containing substrates from corrosion include permeability to water and oxygen, ion migration through the coating film, electrical resistance of the coating, adhesive performance under wet conditions, alkali resistance, the presence of materials which act to inhibit corrosion and the absence of materials which promote corrosion. Such factors have been considered during formulation of oil-base surface coatings and paints. However, it is difficult to formulate waterborne paints, particularly water-dispersible (latex) paints having a high corrosion protection property. The inability to readily formulate corrosion-protective and latex paints is a significant drawback since oil-base paints are being phased out due to environmental restrictions limiting the volatile organic compounds (VOC) content of paints.